Dynamical influences of high viscosity in the lower mantle induced by the steep melting curve of perovskite: effects of curvature and time dependence

Recent experiments on the melting temperatures of perovskite have indicated a high melting temperature in the lower mantle. This suggests that a creep law with an activation enthalpy, that increases strongly with depth, should be employed for the lower mantle rheology. The dynamical consequences of employing an Arrhenius type of dependence in a Newtonian flow law under the Weertman assumption relating activation enthalpy to the variation of the melting temperature with pressure is examined. An outstanding dynamical feature is the presence of a local viscosity maximum with a magnitude of around 10²³Pa.s for Earthlike surface Nusselt numbers between 10 and 15. This viscosity maximum is found in the middle of the lower mantle. There are no small-scale instabilities developed in the D″ layer of these models, thus suggesting that any small-scale lateral heterogeneities existing there may have chemical origins. -from Authors